Quaternary ammonium hydroxides in foam rubber



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United States Patent QUATERNARY AMMONIUM HYDROXIDES IN FOAM RUBBER Robert J. Hay, Fall River, Mass., assignor to The Firestone Tire & Rubber Company, Akron, Ohio, a corporation of Ohio No Drawing. Application January 8, 1954 Serial No. 403,067

8 Claims. (Cl. 260-25) This invention relates to the production of foam rubber by frothing a rubber latex and more particularly to the production of a foam rubber having improved properties. This application is a continuation-in-part of my earlier copending application Serial Number 300,344, filed July 22, 1952, and now abandoned.

In the formation of foam rubber, a rubber latex containing vulcanizing ingredients, desired compounding ingredients and a gelling agent is conventionally converted to a froth or foam by whipping or beating air into the latex. The frothed latex is then introduced into a mold of a desired shape or spread on a continuously moving fiat surface and allowed to set to an irreversible gel. The gelled froth is thereafter subjected to vulcanizing conditions to produce a desired foam rubber article.

The rubber latex used to produce foam rubber may be a natural rubber latex, or it may be a synthetic rubber latex, or it may be a mixture contining natural rubber and one or more synthetic rubber latices. Typical of the synthetic rubber latices is GR-S latex which is produced by aqueous emulsion polymerization of a major proportion of 1,3-butadiene and a minor proportion of Other synthetic rubber latices, also suitable for polymerization of 1,3-butadiene or the other conjugated dienes such as piperylene, dimethyl butadiene, isoprene, 2-chloro-1,3-butadiene and similar compounds either alone or with each other or along with one or more polymerizable ethylene derivatives, for example, acrylic nitriles such as acrylonitrile, methacrylonitrile, alphachloro acrylonitrile; vinyl aromatic compounds such as the various styrenes, vinyl toluene, vinyl naphthalene and the like; and esters and amides of acrylic acids such as methyl acrylate, methyl methacrylate, acrylamide and All of these latices including both natural rubber latex and the above synthetic rubber latices may be suitably designated as rubbery conjugated diene polymer latices. The gelling agent utilized in the production of foam rubber is advantageously a delayed action gelling agent such as an alkali metal silico fluoride, certain ammonium salts such as ammonium nitrate and ammonium sulfate or the like.

Many difi'iculties arise in the production of foam Slight variations in latex, compounding ingredients, maturation and general methods of handling the latex will produce widely varying results. A particular difficulty occurring in the production of foam rubber is a tendency of a frothed latex to collapse or shrink at gelation. Another particular difficulty in the production of foam rubber arises from the conventional use of zinc oxide as a vulcanization aid-zinc ions tend to form complexes which have a destabilizing effect on ''a latex compound. This often results in premature coagulation of the latex and consequent extensive shutdown of factory equipment for cleaning purposes.

An object, therefore, of this invention is to provide a frothed rubber latex which does not collapse at gelation.

a Patented Feb. 4, 1958 Another object is to produce a rubber latex compound which is relatively stable to zinc oxide. Another object is to provide a foam rubber having improved structure. Another object is to provide a method of producing improved foam rubber.

The above and further objects are achieved in accordance with the invention by incorporating vulcanizing ingredients, a gelling agent and a relatively small proportion of a quaternary ammonium hydroxide into a rubber latex of the type generally described in the early portion of this specification, frothing the latex, allowing the froth to set to an irreversible gel and thereafter vulcanizing the gel.

The quaternary ammonium hydroxides useful in the practice of the invention are represented structurally by the following formula:

wherein at least one of R R R and R is an aliphatic hydrocarbonradical and the remainder of said R R R and R are monovalent, or two together are a divalent organic radical, or the nitrogen forms a part of a heterocyclic ring.

Many of the preferred quaternary hydroxides are those wherein one R group constitutes a long alkyl chain containing four or more and preferably six or more carbon atoms and the other R groups are methyl groups or substituted methyl groups. However, as previously indicated, many quaternary ammonium hydroxides are useful in producing the desirable results of the invention. Illustrative quaternary ammonium hydroxides which produce the results of the invention are:

Dodecyl tri (Z-hydroxyethyl) ammonium hydroxide Benzyl trimethyl ammonium hydroxide N-cetyl pyridinium hydroxide Cetyl dimethyl ethyl ammonium hydroxide N-lauryl pyridinium hydroxide Dioctadecyl dimethyl ammonium hydroxide Lauryl imidazoline hydroxide Cetyl trimethyl ammonium hydroxide N-octadecyl dimethyl benzyl ammonium hydroxide Butyl trimethyl ammonium hydroxide Amyl trimethyl ammonium hydroxide Dodecyl trimethyl ammonium hydroxide Octadecenyl trimethyl ammonium hydroxide Octadecadienyl trimethyl ammonium hydroxide Lauryl isoquinolinium ammonium hydroxide Hexadecyl trimethyl ammonium hydroxide Decyl trimethyl ammonium hydroxide 4-cyclohexylbutyl trimethyl ammonium hydroxide 4-phenylbutyl trimethyl ammonium hydroxide Dodecyl trimethyl ammonium hydroxide Tetradecyl trimethyl ammonium hydroxide Octadecyl trimethyl ammonium hydroxide Octyl trimethyl ammonium hydroxide Decyl trimethyl ammonium hydroxide Cetyl dimethyl benzyl ammonium hydroxide Octadecenyl ethyl dimethyl ammonium hydroxide In the practice of the invention, a single quaternary ammonium hydroxide, or if desired, a mixture of two or more different quaternary ammonium hydroxides is added in an aqueous solution or aqueous dispersion to a latex. Only relatively small amounts of the quaternary hydroxides are required to produce the desirable results of the invention. The quaternary ammonium hydroxides are ordinarily used in amounts by weight of 'the order of about 0.1% to about 3.0% of the dry rubber content of the latex but are effective in larger or smaller amounts.

The practice of the invention .is particularly .efiective in preventing foam collapse .at gelation, in reducing gel shrinkage, in preventing the formation of blow holes in a foam rubber article and 'in producing a foam lrubber having an unusually :fine uniform continuous structure.

The practice of the invention is particularly adapted to the production-of foam rubberfro'm natural.rubber synthetic rubber latex blends containing a major proportionof natural rubber latex but is also useful in the production of foam rubber from 100% =naturalrubber latex, from 100% synthetic rubber latex or from blended natural -rubbersynthetic rubber latex wherein the synthetic rubcompounding materials may be used if desired.

A better understanding of the invention can be had by reference to the following examples included for thepurpose of illustrating but not limiting the invention. Throughout the examples, the weight of latex, whether natural or synthetic, is expressed as dry rubber weight.

Example 1 Concentrated natural rubberlatex is compounded according to the following recipe:

Parts by weight Latex (about 60% total 'solids) 100.00 Potassium oleate 2.00 Sulfur 2.00 Accelerator 0.50 Paraffin wax"- 4.00 Benzyl trimethyl ammonium hydroxide 0.25

Four parts by weight of zinc oxide and two parts by weight of sodium silicofiuoride, both based on the weight of rubber, areadded to the above latex'com'pound. The compounded latex is frothed-by-mechanical agitation and the froth is introduced into 'a suitable mold. The froth forms a stable gel after from '3 to 4 minutes and'upon subjecting the gel to vulcanizing conditions an excellent foam rubber results which has a fine-continuous structure. By continuous structure I mean thatthe foam rubber "has essentially no looseends. A latex compound containing no quaternary ammonium hydroxide but otherwise identical with the above compound exhibits complete "foam collapse at gelation.

Example 2 A blend 'of natural and'synthetic rubber latices is compounded in accordance with the invention as follows:

Parts by weight The preparation of the above compound, the addition of zinc oxide and sodium silicofluoride, the frothing of the compound and the gelling and vulcanizing of the "resulting froth Jare carried out in the same manner utilized :in Example 1. Atgelation, 'anexcellent'firm gel results. Upon curing, amexcellent foam rubber having a-fin'e con- .an'nuous-rstructure results. Hereto'o, a compoundi'dentical with the above compound, except that it contains no lowed to gel. gelation. quaternary ammonium hydroxide but otherwise identical 4 quaternary ammonium hydroxide, undergoes foam collapse at gelation.

Example 3 As another illustration of the practice of the invention, a latex compound is prepared which differs only from the compound of Example 2 in that it contains a different synthetic rubber latex. In this instance, polybutadiene latex is used in lieu of the GR-S latex of Example 2. The polybutadiene latex is produced by the polymerization of an aqueous emulsion of butadiene-LS at 120" F. in a rosin soap-potassium oleate system in the presence of a persulfate catalyst. This compound also, when treated with zinc oxide and sodium silicofluoride, produces after frothing and gelling a firm stable gelled froth. Upon vulcanization of'the gelled froth, 'an'exce'llent foam rubber results having a fine continuous structure.

Example 4 Concentrated natural rubber latex is compounded according'to the following recipe:

Parts by weight Three ,parts by weight of zinc oxide and 1.1 partsby weight of sodiumsilicofiuoride, both based on the weight of rubber are added to the above latex compound. The compounded latex is frothed by suitable mechanical means and the froth is introduced into a suitable mold and al- The froth undergoes partial collapse 'at A latex compound, however, containing he with the above compound exhibits complete foam collapse atgelation. Thepresent example is an illustration of the fact that short chain quaternary ammonium hydroxides are elfective in reducing foam collapse at gelation .although they are not elfective to entirely eliminate foam collapse as the preferred long chain quaternary ammonium hydroxides.

Example 5 .An illustration of the practice of the invention with a different quaternary ammonium hydroxide is shown by the use of the following recipe:

Parts by weight Natural rubber latex (60% total solids) 100.00 Potassium 'nleate 2.00 Sulfur 2.00 Accelerator 1.50 Antioxidant 1.00

Octadecenyl ethyl dimethyl ammonium hydroxide 0.25

Three partsby weight of .zinc oxide and 1.1 parts by weight of sodium silicofiuoride are added to the above :foam collapse at gelation.

Example 6 As an illustration of thepractice of the invention with a "st1ll different quaternary ammonium hydroxide another latex compound is prepared which ditfers only from the compounds used inExamples-4 and 5 in that it'contains "a different quaternary ammonium hydroxide. :In this -n'istanc'e, 035 part by weight of cetyl dimethyl ammonium hydroxide per parts latex is used. The

addition of zinc oxide and sodium silicofiuoride and the Natural rubber latex (about 60% total solids) 80.00 Polybutadiene latex 20.00 Potassium l at 2.00 Sulfur 2.00 Accelerator 1.50 Antioxidant 1.00 Cetyl dimethyl ammonium hydroxide 0.25

1 The same type of polybntadiene latex used in Example 3.

Three parts by weight of zinc oxide and 1.2 parts by weight of sodium silicofiuoride are introduced into the above compound and the resulting mixture is whipped to a froth. The froth is allowed to gel and at gelation is stable and firm. Upon vulcanization, an excellent foam rubber having a fine continuous structure is obtained. A latex compound containing no quaternary ammonium hydroxide but otherwise identical with the above compound undergoes substantial surface breakdown at gelation.

Example 8 Another latex compound is prepared according to the same recipe used in Example 7 except for the use of a different quaternary ammonium hydroxide-octadecenyl ethyl dimethyl ammonium hydroxide. When zinc oxide and sodium silicofiuoride are incorporated into this mixture and the mixture is frothed and allowed to gel in the same manner used in Example 7 the froth at gelation is quite stable. After vulcanizing a foam rubber is obtained which has an excellent fine structure. A latex compound which contains no quaternary ammonium hydroxide but is otherwise identical with the above compound exhibits substantial surface breakdown at gelation.

In the claims:

1. A method of producing a foam rubber having a particularly fine continuous structure from a rubbery conjugated diene polymer latex which comprises incorporating into said latex a fatty acid soap, vulcanizing ingredients including sulfur and zinc oxide, an alkali metal silicofiuoride as a latex gelling agent and about 0.1% to about 3.0% by weight of the dry polymer content of said latex of a quaternary ammonium hydroxide having the formula wherein the group of radicals consisting of (1) R R R and R are selected from, the group consisting of alkyl, hydroxy-alkyl and hydrocarbon-substituted alkyl radicals and (2) one of said R R R and R is selected from the group consisting of alkyl and hydrocarbonsubstituted alkyl radicals and the remaining three of the said R R R and R are joined together as a chain of hydrocarbons with N to form a heterocyclic ring, frothing the latex, allowing the resulting froth to set to an irreversible gel and thereafter vulcanizing the gelled froth.

2. An irreversible gelled rubbery conjugated diene 6 polymer latex froth containing a fatty-acid soap, vulcanizing ingredients including sulfur and zinc oxide, an alkali metal silicofiuoride as a latex gelling agent and about 0.1% to about-3.0% by weight of the dry polymer content of said latex of a quaternary ammonium hydroxide having the formula R2 Rr-bI-Ra OH- I wherein the group of radicals consisting of (1) R R R and R are selected from the group consisting of alkyl, hydroxy-alkyl and hydrocarbon-substituted alkyl radicals and (2) one of said R R R and R is selected from the group consisting of alkyl and hydrocarbonsubstituted alkyl radicals and the remaining three of the said R R R and R are joined together as a chain of hydrocarbons with N to form a heterocyclic ring.

3. A method of producing a foam rubber having a particularly fine continuous structure from a rubber latex containing synthetic rubbery conjugated diene polymer which comprises incorporating into said latex a fatty acid soap, vulcanizing ingredients including sulfur and zinc oxide, an alkali metal silicofiuoride as a latex gelling agent and about 0.1% to about 3.0% by weight of the dry polymer content of said latex of a quaternary ammonium hydroxide having the formula r Rr-Ii-Ra OH- wherein the group of radicals consisting of 1) R R R and R, are selected from the group consisting of alkyl, hydroxy-alkyl and hydrocarbon substituted alkyl radicals and (2) one of said R R R and R is selected from the group consisting of alkyl and hydrocarbon-substituted alkyl radicals and the remaining three of the said R R R and R are joined together as a chain of hydrocarbons with N to form a heterocyclic ring, frothing the latex, allowing the resulting froth to set to an irreversible gel and thereafter vulcanizing the gelled froth.

4. A method of producing a foam rubber having a particularly fine continuous structure from a latex mixture containing natural rubber and synthetic rubbery conjugated diene polymer, which comprises incorporating into said latex mixture a fatty acid soap, vulcanizing ingredients including sulfur and zinc oxide, an alkali metal silicofiuoride as a latex gelling agent and about 0.1% to about 3.0% by weight of the dry polymer content of said latex of a quaternary ammonium hydroxide having the formula r Ri-N-Rs OH- wherein the group of radicals consisting of (1) R R R and R are selected from the group consisting of alkyl, hydroxy-alkyl and hydrocarbon-substituted alkyl radicals and (2) one of said R R R and R is selected from the group consisting of alkyl and hydrocarbon-substituted alkyl radicals and the remaining three of the said R R R and R are joined together as a chain of hydrocarbons with N to form a heterocyclic ring, frothing the latex, allowing the resulting froth to set to an irreversible gel and thereafter vulcanizing the gelled froth.

5. A method of producing foam rubber having a fine continuous structure, which comprises incorporating a fatty acid soap, rubber vulcanizing ingredients including sulfur and zinc oxide, an alkali metal silicofiuoride and benzyl trimethyl ammonium hydroxide into a rubbery conjugated diene polymer latex, frothing the latex, allowing the frothed latex to set to an Irreversible gel and thereafter vulcanizing the gelled froth, said benzyl trimethyl ammonium hydroxide constituting about 0.1% to 7 about 330% by weight of the dry polymer content of said latex.

6. A method of producing foam rubber having a fine continuous structure, which comprises incorporating a fatty acid soap, rubber vulcanizing ingredients including sulfur and zinc oxide, an alkali metal silicofluoride and cetyl trimethyl ammonium hydroxide into a rubbery conjugated diene polymer latex, frothing the latex, allowing the frothed latex to set to an irreversible gel and thereafter vulcanizing the gelled froth, said cetyl trimethyl ammonium hydroxide constituting about-0.1% to about 3 .0% by weight of the dry polymer content of said latex.

7. A method of producing foam rubber having a fine continuous structure, which comprises incorporating a fatty acid soap, rubber vulcanizing ingredients including sulfur and zinc oxide, an alkali metal silicofluoride and octadecenyl ethyl dimethyl ammonium hydroxide into a rubbery conjugated diene polymer latex, frothing the latex, allowing the frothed latex to set to-an-irreversible gel and thereafter vulcanizing the gelled froth, said octadecenyl ethyl dimethyl ammonium hydroxide constituting 8 about0.1% to about 3L0%- by weight of the dry polymer content of said latex.

8. A method of producing foam rubber having a fine continuous structure, which comprises incorporating a fatty acid soap,- rubber vulcanizing ingredients including sulfur and zinc oxide, an alkali metal silicofiuoride and tetra-ethyl ammonium hydroxide into a rubbery conjugated diene polymer latex, frothing the latex, allowing the frothed latex to set to an irreversible gel and thereafter vulcanizing the gelled froth, said tetra-methyl ammonium hydroxideiconstituting about 0.1% to about 3.0% by'weight of:the drypolymer content of said latex.

References Cited in the file of this patent UNITED STATES. PATENTS 2,242,223 Bley May 20, 1941 2,261,439 Kelly Nov. 4, 1941 2,321,111 Stamberger June 8, 1943 2,375,089 Ebers May 1, 1945 2,426,430 Binns Aug. 26, 1947 2,580,473 Sowaet al, Ian. 1, 1952 

1. A METHOD OF PRODUCING A FOAM RUBBER HAVING A PARTICULARLY FINE CONTINUOUS STRUCTURE FROM A RUBBER CONJUGATED DIENE POLYMER LATEX WHICH COMPRISES INCORPORATING INTO SAID LATEX A FATTY ACID SOAP, VULCANIZING INGREDIENTS INCLUDING SULFUR AND ZINC OXIDE, AN ALKALI METAL SILICOFLUORIDE AS A LATEX GELLING AGENT AND ABOUT 0.1% TO ABOUT 3.0% BY WEIGHT OF THE DRY POLYMER CONTENT OF SAID LATEX OF A QUATERNARY AMMONIUM HYDROXIDE HAVING THE FORMULA 